Thermionic amplifier



B. VAN DER POL r:r m. 1946,047

THERMIONIC AMPLIFIER Feb. 6, 1934.

Fild Feb. 16, 1931 ATTORNEY Patented Feb. G, 1934 THERMIQNIC AMPLIFIER Balthasar van der Pol, Klaas Posthumus, am!

Dominicus Eindhoven, Netherlands, assignors to Radio Corporation of America, a corporation 'of Dela- Bernardus Ware ' Application February This invention relates to thermionic amplifiers and has for its purpose to render the current or voltage variations in the output circuit proportional to the vo1tage amplitudes 01 the incoming oscillations for all frequencies. In all amplification stages of the usual circuit arrangements in Which resistances other than pure ohmic resistances are used in the output circuits oscillations of difierent frequencies are unequa1ly amplified. According to the invention part of the output impedance is coupled with the input circuit such that for all frequncies the alternating current set up in the output impedance or the alternating voltage set up between the terminals of this im- -pedance are proportional to the voltage anaphtudes of the incoming oscillations. Besides the signal voltages there am supplied voltages to the input circuit which, dependent on the fact whether an intermediate amplifier or a terminal amplifier is provided, are dependent 0n the eurrent or voltage variations set up in the output-cireuit. With intermediate amplifiers it is desired that equa1 voltage variations at the input circuit Wi11 cause equal voltage variations at the output Y circuit independently of the frequency. With terminal amplifiers it is required, on the contrary, that the current variations set up in the output circuit are the same for different frequencies. When considering in general amplifying circuit with back-coupling in which Rx=the internal resistance of the tube Ru=the external resistance s=the slope 01 the characteristic curve. g=the amplification factor m.==the anode alternating voltage ia=the anode alternating current v s=grid potential set up by signals v x=grid potential set up by back coupling i.t follows that 1 1 a us+ V02) By selecting so that Ua is proportional to 'Ugs, which is required 5D; in intermediate ampliflers. The va1ue of and. consequently proportional to that 01 the anode current.

1a, 1931, Serial N0516,108,V and in the Netherlands February 14, 1930 2 Claims. (01179-171) Hubertus Tellegen,

' By seleoting on the contrary x 1 -sv so that ia is proportional to 'Dgs which is desirable 5 in terminal arnplification. In this case the value of the electro-motive force to be ooup1ed back is determined by g and consequently proportional to the anode a1 ternating voltage.

'Ihe invention will be more clearly understood. by reference to the accompanying drawing, representing, by way of example, some embodiments of the invention.

Figs. 1 and. 2 show terminal amplification circuit arrangements; and,

Fig. 3 a circuit arrangement of an intermediate amplification stage. v

In Fig. 1 in the output circuit of the thermionic tube 1 a transformer 2 is interposed whose primary side is connected in series with a loudspeaker 3. The voltages set up in the secondary winding of this transformer are supplied. to the grid. 01 the tube in series W'1th the signal voltage. New the ci1cuit arrangement is such that the electromotive force which is coupled. back is in opposi tion 01 phase to the pressure variations set up in the output circuit, whereas the value is g By connecting a potentiometer 4 across the secondary of the transformer the back-coupling is rendered regulable.

Fig. 2 shows a terminal amplification circuit arrangement in which the energy is supplied to the loudspeaker across a transformer 5. This transformer may serve at the same time for the back-coupling by providing an extra tap 6 at 109 the primary side. This tap is connected to the filament, whereas the portion, 6, 7 cf the primary winding (if desired a portion thereof across a potentiometer 8) is connected in series with the grid circuit. In Fig. 1 the electro-motive force which is coupled back equals again just as in Fig. 1. 119

Fig. 3 shows an i'ntermediate amplification stage. In the output circuit 015 the thermionic tube 1' an ohmic resistance is connected in series with a coupling impedance 9 (for example a transformer) The voltages Set up between the points 11 and 12 of this resistance are proportiona1 to the currents 'circulating in ehe transformer 9. These voltages are returned 1:0 the grid o1 the thermionic tube through a transformer 13 having a ratio of transformation 1:1. Gare is to be taken that the impedanee 0f the transformer 13 is great relatively to the ohmic resistance cf 10, so that the voltage betvveen the points 11 and 12 practically depends on1y on this ohmic resistance, in other words is directly proportional 110 ia. By the transformer 13 the polarity of the voltage is reversed again, whereas by displacing the tap 11 along the resistance the valueof the voltage which is coupled back may be adjusted.

We claim:

1. In an amplifier cirouit a space discharge device having an input circuit and an output circuit, said output circuit including a coupling impedance and a resistance element in series, a

transformer having i'ts primary shunted' across at least a portion of said resistance and its secondary included in said input circuit, the irnpedance of said transformer beim; of such a va1ue relative t'o the ohmic resistanc'e of said element that the voltage across said element depends subste'mtially only upon the drop across the resistance element.

2. In an amplifier circuit a space discharge dev1ce having an input circuit and an output circuit, said output circuit including a coupling impedance and a resisfiance element in series, a transformer having its primary shuntedacross ab least aportion of said resistance and its secondary included in said input circuit the impedance of said transformer being high relative 110 the impedance of said resistance element whereby ehe voltage across the Glement depends .substantially only upon the drop across the resistance element.

BALTHASAR' VAN DER POL. KLAAS POSTHUMUS. BERNARDUS DOMINICUS HUBERTUS TELLEGEN. 

